Power over Ethernet (PoE), in accordance with both IEEE 802.3af-2003 and IEEE 802.3at-2009, each published by the Institute of Electrical and Electronics Engineers, Inc., New York, the entire contents of each of which is incorporated herein by reference, defines delivery of power over a set of 2 twisted wire pairs without disturbing data communication. The aforementioned standards particularly provide for a power sourcing equipment (PSE) and a powered device (PD).
When a PD no longer draws power from the PSE, defined by the above mentioned standard as the lack of a maintain power signature (MPS), the PSE shuts down within a predetermined time period and periodically performs a detection stage to detect if a valid PD is connected to the PSE. In the event that a valid PD is detected, the PSE is arranged to supply power to the PD, optionally after performing a classification stage to determine the class of the PD. For some applications, such as lighting, the period between successive detection stages is longer than a user is willing to wait for. As a solution, the PD may be arranged to continuously draw a predetermined minimum amount of power from the PSE so as to maintain the MPS. In order to keep the PSE from shutting down, a direct current (DC) DC MPS is defined in the IEEE 802.3af-2003 standard as sinking at least 10 mA for a minimum duration of 75 ms followed by a dropout period of no more than 250 ms. Unfortunately, this constitutes a significant amount of wasted power, approximately 150 mW. In particular, any control electronics, e.g. a remote control switch, motion detectors, ambient light sensors and network cards, do not need such large amounts of power, thereby most of it is wasted. In the absence of an MPS, a command to energize a PoE based PD will not be actively responded until the next detection, optional classification, and powering cycle occurs. Such a cycle is typically performed every 1-2 seconds, which is not acceptable for lighting. Furthermore, power for any remote control receiving apparatus is not available from the PSE, unless the MPS is maintained.
There is thus a long felt need for a PoE system which can provide rapid turn on of a PD without drawing a large MPS.